1. Field of the Invention
The present invention relates to an optical system, an optical module, and a method of manufacture thereof.
2. Background of the Invention
Conventional autofocus or zoom systems of Optical system require a set of lenses and large space because of mechanical motors. Recently, a MEMS-based motion control stage is used to minimize the space of mechanical motors. However, manipulation of the space between lenses is not the only way to change the effective optical power. It also could be done by either varying the surface curvature or changing the refractive index distribution. These methods can be generally divided into refractive type and reflective type. Liquid lens and liquid crystal lens (LC lens) belong to refractive type. Liquid lens adopts bi-liquid lenses that can deform the shape of the interface between two immiscible liquids by electro-wetting method. Liquid crystals (LCs) are excellent electro-optic materials with electrical and optical anisotropies. The optical properties can be controlled easily by external electric field. According to the change of refractive indices, the light can be converged and diverged. However, both liquid lens and liquid crystal lens need to utilize refractive design forms that require straight optical path. This fundamentally limits packaging thickness.
Another solution is reflective type, which adopts MEMS deformable mirrors (MEMS DM) to vary the optical power by deforming reflecting surfaces. The advantage of reflective type is chromatic aberration free. Besides, the straight optical path can be folded to reduce packaging thickness. DMs could be embedded with wave front sensors to correct the wavefront aberration for astronomical observation. The system is commercialized for years. Traditionally, MEMS DMs are made by inorganic materials, such as silicon or silicon nitride. These materials have high mechanical stiffness, which limits their deformation range. The deformation of MEMS DM presented in this paper is about one order of magnitude higher than commercial products. In this paper we propose an optical system using a polymer MEMS DM in a reflective design form. The polymer MEMS DM could achieve 12-μm displacement over a 3-mm aperture that corresponds to about 20 diopter focusing power. The optical layout design is 5.4 mm thick and 6.7 mm after packaging. The optical system design, performance analysis, experimental results are discussed in following sections.